The incidence of hospitalization for the removal of urinary calculi, commonly referred to as kidney stones, has been estimated to be as high as 200,000 cases per year. A vast majority of these patients pass their stones spontaneously; however, in the remainder, the kidney stone(s) become impacted in the ureter, a muscle tube joining the kidney to the bladder. An impacted kidney stone is a source of intense pain and bleeding, a source of infection and, if a stone completely blocks the flow of urine for any extended length of time, can cause a loss of a kidney. Small stones which are lodged in the lower one third of the ureter can frequently be removed non-surgically using a technique employing a well known Dormia stone basket. This procedure is successful in approximately 50% of the cases. However, basket removal of a kidney stone usually fails if the stone is lodged in the upper ureter, is impacted, or is in the order of 1.O cm in size. In these cases the only procedure by which the stone could heretofore be removed was through a major operation called a ureterolithotomy.
More recently, however, a non-surgical method for removing kidney stones has been developed wherein a catheter is placed cystoscopically at the site of the stone in the urinary tract, after which a long wire probe, acting as an ultrasonic waveguide, is passed through a lumen of the catheter and is brought into contact with the stone. The wire probe is attached to an ultrasonic transducer which, when energized, sets the wire probe into longitudinal and transverse vibrations. The vibrational energy is transmitted to the stone, causing it to fracture into small fragments which the patient can then pass spontaneously after withdrawal of the catheter.
While such apparatus is adapted to operate as intended, a severe limitation has been found to exist due to premature breakage of the wire probe at the point of connection to the tip of the ultrasonic transducer. The vibrational energy, typically 20KHz in frequency, causes the wire probe to snap off after 15 or 20 seconds of operation. This has been found to be insufficient time to complete a kidney stone disintegration procedure, even though the stone will fracture after as little as about 10 seconds of contact with the wire probe. What is required is a means to prolong the operational life of the wire probe for a length of time adequate for completion of the procedure. A desirable time frame is typically 1 minute, which is an order of magnitude greater than that currently provided by known prior art apparatus.